This invention relates generally to a cutting tool for removing stationary man-made objects or tubular materials downhole from a well bore, such as packers stuck downhole, cemented casing, cemented tubing inside casing, cement aggregates, jammed tools or the like, and more particularly, to such a cutting tool having at least a portion of the blades extending from the bottom of the tool body and being inserted within a well bore for removing the members by first reducing the members to turnings or small chips for removal from the well by drilling fluid.
Heretofore, cutting tools have been provided with blades having at least a portion of the blades extending from the bottom of the tool body for cutting away a stationary object in a well bore such as a packer or cemented casing. However, such prior blades have been formed with tungsten carbide cutting fragments or chips embedded in a random pattern in a matrix formed of a suitable powder metallurgy composite material such as sintered tungsten carbide in a cobalt matrix to provide the cutting surface, and the cutting elements heretofore have not been arranged or constructed to provide a "chip breaker" action. As an example of such a cutting tool, rotary shoes having blades extending from the bottom and side of the tool body and utilizing crushed tungsten carbide particles in a matrix have been used in cutting away packers stuck downhole in a stationary position. However, particularly when the packers have been formed of a high strength corrosion resistant alloy steel, a glaze or work hardened surface is formed when being cut by such rotary shoes which is difficult to cut further and results in an abnormally low rate of penetration for the cutting tool.
Milling or cutting tools heretofore having blades extending from the tool body and formed with the tungsten carbide chips embedded in a matrix have normally utilized blades for taking a relatively small thickness bite from the man-made stationary metal object to be removed which provides a conglomeration of shapes and sizes of metal turnings ranging from fine hair-like turnings to curlings of around 6 inches in length, for example. Such turnings tend to curl and internest with each other to provide a so-called "bird nest" or mass which is difficult to remove from the well bore by drilling fluid after being cut from the metal object. The critical factor in obtaining a high rate of penetration is in the removal of the metal scrap material and oftentimes the limiting factor in the cutting operation is the rate of removal of the metal scrap material. Long relatively thin turnings or shavings tend to restrict such removal rates by internesting and wrapping around the drill string. The utilization of cutting elements or chips in a random pattern provides a non-uniform cutting action and this likewise tends to restrict the rate of cutting or milling away of the stationary object downhole.